In a food processor, combine flour and powdered sugar. Add cold butter, pulsing until resembling coarse crumbs. Mix in egg yolk and water to form a dough. Chill for 30 mins.

Preheat oven to 350°F (175°C). Roll out dough, press into mini tart pans, prick bottoms, and bake for 10–12 mins until golden. Cool completely.

Whisk together lemon juice, lemon zest, sugar, and eggs in a saucepan over medium heat until thickened, about 8-10 mins. Stir in butter until melted. Pour into cooled tart shells and chill for at least 1 hour.

Set up a double boiler and whisk egg whites, sugar, and cream of tartar until warm, about 2-3 mins. Whip on high speed until stiff peaks form. Fold in vanilla and violet food coloring.

Using a kitchen torch, toast the meringue on tarts until golden. Garnish with lilac petals or lavender before serving.